Methods for fabricating stepped etalons

Abstract

The specification describes stepped etalon structures and techniques for their fabrication. The preferred etalon material is LiCaAlF 6 , which is not efficiently processed using reactive ion etching. The approach of the invention is to produce the steps on the etalon by depositing a blanket layer of step material that is effectively etched by RIE, masking a portion of the step material, and etching the masked blanket layer using the LiCaAlF 6 substrate as an etch stop. These process steps may be repeated to form multiple steps on the etalon. Etalon structures with steps on both major surfaces are described, as well as etalon structures with steps having differing areas. In the latter case a difference in amplitude in the output signal from a single detector can be used to identify the step that is resonating.

We claim:  
     
       1. A process for making a stepped etalon comprising the steps of: 
       (a) depositing a first step layer on a first surface of a transparent substrate, the transparent substrate having a figure of merit F o <5e−6 over the wavelength range 1500-1600 nm and the temperature range 10° C. to 30° C., and the first step layer and the transparent substrate comprising different materials,  
       (b) masking a first portion of the first step layer leaving an exposed portion of the step layer,  
       (c) etching the exposed portion of the first step layer by an RIE process at a rate of greater than 500 Angstroms per minute leaving a first step, and leaving an exposed portion of the transparent substrate the exposed portion of the transparent substrate etching at a rate of less than 200 Angstroms per minute.  
     
     
       2. The process of  claim 1  wherein the substrate has a second surface, with the first and second surfaces parallel, and wherein the second surface is processed by steps comprising: 
       (a) depositing a first step layer,  
       (b) masking a first portion of the first step layer leaving an exposed portion of the step layer,  
       (c) etching the exposed portion of the first step layer by an RIE process at a rate of greater than 500 Angstroms per minute leaving a first step, and leaving an exposed portion of the transparent substrate the exposed portion of the transparent substrate etching at a rate of less than 200 Angstroms per minute.  
     
     
       3. A process for making a stepped etalon comprising the steps of: 
       (a) depositing a first step layer on a transparent substrate, the transparent substrate having a figure of merit F o <5e−6 over the wavelength range 1500-1600 nm and the temperature range 10° C. to 30° C., and the first step layer and the transparent substrate comprising different materials,  
       (b) masking a first portion of the first step layer leaving an exposed portion of the first step layer,  
       (c) etching the exposed portion of the first step layer by an RIE process at a rate of greater than 500 Angstroms per minute leaving a first step, and leaving an exposed portion of the transparent substrate the exposed portion of the transparent substrate etching at a rate of less than 200 Angstron per minute,  
       (d) depositing a second step layer on the first step and the exposed portion of the transparent substrate.  
     
     
       4. The method of  claim 3  in which the transparent substrate is LiCaAlF 6 . 
     
     
       5. The method of  claim 4  in which the first and second step layers comprise a material selected from the group consisting of SiO 2 , SiN, Al 2 O 3 , TaN. 
     
     
       6. The method of  claim 3  in which the thickness of the first and second step layers is in the range 0.05-3.0 microns. 
     
     
       7. The method of  claim 3  wherein step layer is etched by RIE using a halide plasma. 
     
     
       8. A method for controlling an optical device comprising directing an optical beam from the optical device through a stepped etalon, the stepped etalon produced by steps comprising: 
       (a) depositing a first step layer on a first surface of a transparent substrate, the transparent substrate having a figure of merit F o <5e−6 over the wavelength range 1500-1600 nm and the temperature range 10° C. to 30° C., and the step layer and the transparent substrate comprising different materials,  
       (b) masking a first portion of the first step layer leaving an exposed portion of the step layer,  
       (c) etching the exposed portion of the first step layer by an RIE process at a rate of greater than 500 Angstroms per minute leaving a first step, and leaving an exposed portion of the transparent substrate the exposed portion of the transparent substrate etching at a rate of less than 200 Angstroms per minute.